In Africa and Europe stone tools are seen to increase in complexity over the last few million years, says Szabo.

But in East Asia, Southeast Asia, Australia and New Guinea, stone tools don't appear to develop until the last 4000 years.

She says this has led to the conclusion by some that this region was "static", with some dubbing it "culturally retarded".

Some archaeologists argue that, like the hunter gatherers of today, humans in Australasia relied on plants, such as bamboo, rather than stone, and these aren't preserved in archaeological record.

"That may very well be true but we can't prove it," says Szabo.

She says researching shell is exciting because it can be preserved for just as long as stone in the archaeological record.

"It's not a material that anyone's looked at or that anyone particularly understands very well," says Szabo.

Indonesian excavation

In published research to date, Szabo reports having excavated shell tools dating back 32,000 years from a cave site in eastern Indonesia, and comparing them with stone tools from the same cave.

"It transpired that the shell tools were in fact much more complex to produce than the stone tools," she says.

The stone tools were randomly chipped, but the shell tools had been carefully chosen and shaped.

In one case, a "catseye" or operculum shell was flaked systematically with five blows, each one slightly overlapping with the last in a clockwise direction.

In another, a limpet shell was used as a scraper, resulting in a smooth edge.

Flexible humans

Szabo says these finding suggest humans in Australasia were using shell, rather than stone as their raw material of choice.

She says, this made sense because while Europe has high quality flint. Australasia generally has very poor quality stone, but a high diversity of marine molluscs.

"The story is that stone tools should encapsulate the story of humanity," says Szabo.

"But if we're an adaptable, flexible species, living in a range of habitats around the world from the subarctic to the humid tropics, then we should really expect to see a lot of variation in the way that humans are going about solving problems."

Szabo says there has been some debate among archaeologists over what qualifies as good evidence for shell tools.

She emphasises shell does not fracture the same way as stone tools. Therefore they need to be analysed using different protocols to those usually used to analyse stone tools.

Szabo now plans to re-excavate the Indonesian site to obtain more samples and develop a robust methodology for analysing shell tools.